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Perhaps before you draw conclusions do some testing first. What stuck out for me was when you mentioned timing and that’s where I would be looking but not ignition timing right off instead engine mechanical. To do this remove the distributor cap and bring the engine to TDC #1 cylinder so that you can see the timing mark lined up, do this by hand BTW. Once you have the pointer lined up with TDC and you have the distributor cap off rotate the engine in the opposite direction of normal rotation which would be counterclockwise till you see the ignition rotor start to move, when you do stop rotating the engine and look down and the timing mark, if it has moved more than 7
well eric, i did a basic check of the timing chain stretch just by rotating the water pump pully back and forth. of corse its not anywhere close to exact numbers. but i know it took about an inch, inch an a half of pully travel before the rotor moved. so that tells me the chain and gears are in pretty bad shape. from what i know these engines pretty much ALWAYS need the timing set replaced at 100 thousand miles. (this car is at 140) i know alll about the dumb nylon gear coating… dumbest thing chrysler ever did to an engine, if you ask me.
this could be the problem. i never over looked it. and i for sure want to correct the problem, because i know the chain is an issue, i just dont want to do it in the middle of winter outside… so i am trying to rule out every other possible thing. because to tell you the truth i just have a feeling that isnt what is causing it.
the fluctuating idle i mentioned doesnt always fluctuate. it only changes up and down about 150 rpm or so while warming up. it will start off fast. then about 3-5 minutes later it slows down. and stays that way for 5-10 minutes. then it will speed up again and level off and stay what ever speed i set it at. it really seems like it is being caused by the computer. because there are certain system that come on and off during warm up. and i think it is being caused by that. there is an air injection system. which comes on when first started then shuts off when the engine gets a certain temperature. then erg will come into effect. and also air/fuel metering comes into effect after the o2 sensor gets to 600 degrees. and it effects a “mixture solenoid” inside the carb. this solenoid is basically a plunger with a jet in it. and only changes the the air/fuel ratio while crusing or acclerating. during idle, only the idle circut and idle mixture screws effect the mixture…
i really hate this stuff because its a bastardized way to run a car! its in between new and old technology. and it was never meant to be. it was only slapped together because of government regulations. so i dont really even think you can get this stuff to run right no matter what you do. i am getting very close to giving up on it and just buy an electronic ignition conversion kit for $150-$200. i should have done that in the first place and i could have saved tons of money and time! to make it work truely right though i would need an old style , none feedback carb. but probably as soon as i can find a holley 2280, or carter bbd for real cheap somewhere i can rebuild and slap on, i will do that. i guess i can buy a carter bbd from the parts store for a 74 plymouth valiant 318 for about $150. so thats not too bad. but i am quite broke these days. so im looking for something more like $50!
anyways eric. i seem to always talk your ear off. but i do that with everyone. especially when i get going on cars! haha. but thanks for all you do. its great that you are having the success that you are doing what you love, and want to do. it really is an inspiration. keep it up!
or i forgot to mention. i have also done a complete tune up. plugs, wires, cap, rotor, coil (tested bad) and it has a new air filter….
First, ANYTIME you have a know mechanical issue you need to address it first before you move on to other things when dealing with performance issues. You may be correct in that there is something else causing the idle fluctuation and to be honest those old ‘hybrid’ systems that had electronic controls on carburetors were a real pain and being someone that actually worked on some of those systems before fuel injection came into vogue I can say without a doubt I was happy to see carburetors of that type go away. But more to my point if valve timing fluctuates then your not going to have consistent engine vacuum and without consistent engine vacuum a carburetor is NEVER going to work properly and a loose timing chain is NEVER going to provide consistent engine vacuum. Also I don’t see how rotating the water pump could give you any indication of timing chain slack as it’s not directly connected to the timing chain in any way, I’d recommend rotating the crank shaft as suggested just to be certain but it sounds like you’ve already determined that you have excessive slack in the chain. Nylon gears were used by ALL domestic makes to my knowledge and they did it to quiet the operation of the engine which it did quite well but they did tend to wear out and require replacement quite often and tended to cause a variety of performance issues when they did wear out including ‘pinging’ and idle problems. My suggestion would be to wait till you have warmer weather so that you can replace the timing chain and then recheck for the issues that you’re having, if not any corrections you make to the ignition timing or carburetor will have to be addressed or corrected when you get the engine running right and everything back in time mechanically.
ok Eric. last night i went out and tried to do some more testing on the car. i got it up to operating temperature. then i hooked up a tach/timing light , and then i disconnected the vacuum line that runs from the carburetor base plate to the vacuum transducer on the computer. i hooked a vacuum gauge on end of this line. then i put my vacuum hand pump in place of the regular vacuum line, and hooked that to the transducer. i figured what i would do is see what my vacuum readings looked like, and then put that same amount into the transducer via the pump. all the while checking to see where the timing was. i began to notice that any time i would give the transducer on the computer the same vacuum that my vacuum gauge was showing the engine was producing, it would ping pretty bad. and it would advance the timing farther than i could see. granted the timing scale on this car is pretty stupid. and you cannot tell where its at beyond about 15 degrees advanced. then i started letting vacuum out of the pump slowly. and it would stop pinging when i would get to about 5 in vacuum. problem is the engine was producing about 20-22 inches of vacuum… im really not sure what this means… but i thought it was interesting. also when you set the timing on this car, you are supposed to disconnect the vacuum line from the transducer and plug it. then set timing. because once you plug it back in, it always causes the timing to advance beyond what you can see..
i also tested the timing chain stretch, right. i lined the timing mark up with 0. turning the crank one way. then i turned it the other way till i saw the rotor move. i then looked at the timing scale and the mark had moved about 12-13 degrees! so yeah. i would imagine i really do need to put a timing set on. but i still wonder how that could be making this pre detonation ping? could you explain to me how the chain slack could be causing this issue??? and what, if anything, my vacuum pump test indicated?
i swear. this car is haunted. it gets so irritating. because i will think i have things sorted out, then the next time i go start it up its got a whole new set of issues. its never the same car it seems like. and its like im always chasing my tail with it. never getting anywhere, just going in circles. and testing, and re testing, and coming up with new tests, that im not quite sure what they mean haha… it drives me nuts! i think im just gonna have to do the chain and gears and then see if anything is better. if its still not then i REALLY dont know where to go. looks like ill have to rig up some sort of tarp over top of my car today and try to get this done! along with the foot of snow…
As the cam rotates the lobes are loaded then unloaded as they pass the apex of the lobe, this creates a ‘jerking’ motion as it rotates changing the speed the entire time and offsetting not only the valve timing but also the ignition timing since the distributor is splined to the cam. The fact that you have such a loose chain warrants replacement of that chain before you do anything else as I’ve said before, you, the computer, or anything else cannot compensate for a mechanical issue like that so it needs to be addressed first.
hey Eric, i have a related question. i plan on replacing my timing set but i figure while i do that it would also be a good time to replace my lifters. i have 1 or 2 that tick pretty bad on a cold start. it goes away after the car warms up. it usually only takes a couple minutes. before it stops. what i wonder is how long does that have to usually go on for it to score the cam lobes enough to were you also need to replace the cam? i would love it if i only had to do the lifters. because to replace the cam i would have to take alot of stuff off the front end of the car. i know the only real way to know would be to take the intake off and try and get a look. but i just wonder from your experience does it take long when you have lifter issues for it to damage the cam also? the engine isnt running rough like the cam is worn any… but i just wonder what you have run into with this situation…?
There is only one way to replace lifters and that’s with a cam as they are a matched set, If you replace just one or the other you will accelerate the wear on the one that was not replaced. However if you’re putting a timing set on it it’s really only a couple of fasteners and you’ll have the cam out so it’s really not that big a deal if your going to do the gears and chain anyway. Besides that’s a perfect opportunity to add a little ‘performance’ to the engine with a different cam, it doesn’t have to be radical just a mild upgrade would probably give you real benefits.
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